Along with the rapid distribution of information-related equipment and telecommunication equipment such as personal computers, video cameras and mobile telephones in recent years, more emphasis is put on the development of batteries (for example, lithium batteries) that are excellent as power supplies of the equipment. Furthermore, in fields other than the information-related equipment and telecommunication equipment, for example, in the automotive industry, development of lithium batteries and the like for electric cars and hybrid cars is underway.
Here, in lithium batteries that are conventionally available in the market, since organic liquid electrolytes making use of flammable organic solvents are used, improvements in terms of structure and material are needed for the installation of safety devices that suppress temperature increase at the time of short circuits, or for the prevention of short circuits. In this regard, since an all solid state battery in which the liquid electrolyte has been changed to a solid electrolyte, does not use flammable organic solvents in the battery, it is contemplated that simplification of safety devices is promoted, and excellent production cost or productivity is attained.
In the field of such all solid state batteries, attention has been paid for a long time to the interface of an active material and a solid electrolyte material, and there have been attempts to promote an enhancement in the performance of all solid state batteries. For example, Patent Literature 1 discloses an all solid state lithium battery which uses a lithium ion conductive solid electrolyte containing a sulfide as a main component, the battery having the surface of a cathode active material coated with a lithium ion conductive oxide. This technology is intended to suppress the formation of a high resistive layer that is generated at the contact interface between a sulfide solid electrolyte and a cathode active material.